<!DOCTYPE html>
<title>CSS Anchor Positioning: basic last successful position fallback</title>
<link rel="help" href="https://drafts.csswg.org/css-anchor-position/#last-successful-position-fallback">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="support/test-common.js"></script>
<style>
  #container {
    position: relative;
    width: 400px;
    height: 400px;
    background: teal;
  }
  #anchor {
    position: relative;
    top: 100px;
    left: 100px;
    width: 100px;
    height: 100px;
    background: red;
    anchor-name: --a;
  }
  #anchored {
    position-anchor: --a;
    position-try-fallbacks: flip-block;
    position: absolute;
    width: 100px;
    height: 200px;
    position-area: top center;
    background: lime;
  }
</style>
<div id="container">
  <div id="anchor"></div>
  <div id="anchored"></div>
</div>
<script>
  promise_test(async () => {
    await waitUntilNextAnimationFrame();
    await waitUntilNextAnimationFrame();
    assert_equals(anchored.offsetTop, 200);
  }, "Starts rendering with flip-block");

  promise_test(async () => {
    anchor.style.top = "150px";
    await waitUntilNextAnimationFrame();
    await waitUntilNextAnimationFrame();
    assert_equals(anchored.offsetTop, 250);
  }, "No successful position, keep flip-block");

  promise_test(async () => {
    anchor.style.top = "200px";
    await waitUntilNextAnimationFrame();
    await waitUntilNextAnimationFrame();
    assert_equals(anchored.offsetTop, 0);
  }, "Base position without fallback now successful");
</script>
